Transformer-Less Series Reactive/Harmonic Compensation of Line-Commutated HVDC for Offshore Wind Power Integration

A Review of Hybrid Topologies Combining Line-Commutated and Cascaded Full-Bridge Converters

“…Thus, since the grid voltage is constant under normal operation, from (29) follows that the dc-link voltage of a conventional LCC depends only on the firing angle α. In contrast, the commutation voltage of the SAC topology depends on the voltage that is injected for achieving a specific power angle ϕ, as described by (8). Therefore, the expression of the dc-link voltage for the SAC can be derived by substituting (8) in (29), which yields…”

“…Since the injection of V fa impacts the amplitude of the commutation voltageV ca , ϕ is affected by the injected voltage for a certain α, based on (8). Thus, from (31) it follows that the injected voltage modifies both the active (P hyb ) and reactive (Q hyb ) power of the SAC.…”

“…Recently, the ideas of using a FB VSC as an active capacitor or as a source of voltage pulses have been proposed in [7] and [8] respectively. In [7] it is shown that the capacitance of the full-bridge can be significantly reduced by employing special modulation techniques, which account for variations of the capacitor voltage.…”

“…In [7] it is shown that the capacitance of the full-bridge can be significantly reduced by employing special modulation techniques, which account for variations of the capacitor voltage. In [8] the alternative concept of voltage-pulse injection is analyzed. This concept in this paper is similar to that in [1], [2], with the difference that the voltagepulse injection is implemented by single-phase full-bridge (FB) VSCs and does not require an active energy source.…”

“…This implementation requires less capacitance and is more compact than a CCC. However, the voltage rating of the FB VSC in both [7] and [8] needs to be relatively high, implying the need for series connection of semiconductor devices.…”